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aerosol Particles of matter-- solid or liquid-- larger than a molecule but small enough to remain suspended in the atmosphere (up to 100 µm diameter). Natural origins include salt particles from sea spray and clay particles as a result of weathering of rocks. Aerosols can also originate as a result of human activities and in this case are often considered pollutants. Aerosols are important due to their role as participants in chemical reactions in the atmosphere and as absorbers and scatters of solar radiation, where they are considered to be negative radiactive forcing agents.

Proportion of solar radiation reflected by a surface, often expressed as a percentage or a fraction of 1. Snow-covered areas have a high albedo (0.9, or 90%) due to their white color, while vegetation has a low albedo (0.1, or 10%) due to the light absorbed for photosynthesis. Clouds are the chief cause for variations in Earth's albedo.

Made or induced by humans. Usually used in the context of emissions that are produced as a result of human activities.

In an elliptical orbit, it is the farthest point from the sun.

A mixture of gases surrounding the Earth. Earth's atmosphere consists of 79% nitrogen (by volume), 20.9% oxygen, 0.03% carbon dioxide, and trace amounts of other gases. It can be divided into a number of layers according to thermal properties (temperature). The layer nearest Earth is the troposphere (up to about 10-15 km above the surface), next is the stratosphere (up to about 50 km) followed by the mesosphere (up to 80-90 km) and finally the thermosphere or ionosphere which extends into space. There is little mixing of gases between layers.

biogeochemical cycle
Movement of elements or compounds, such as carbon, through living organisms and the nonliving environment.

The mass of living or organic material, usually expressed as dry weight per unit area.

biomass burning
The burning of organic matter for energy production, forest clearing, and agricultural purposes. Carbon dioxide is a byproduct of biomass burning.

The region inhabited by living organisms on land , in the oceans and in the atmosphere.
The region inhabited by living organisms on land , in the oceans and in the atmosphere.

carbon cycle
The process of removal and uptake of carbon on a global scale. This involves components in food chains, in the atmosphere as carbon dioxide, in the hydrosphere, and in the geosphere. The major movement of carbon results from photosynthesis and from respiration.

carbon dioxide (CO
A molecule formed from one atom of carbon and two of oxygen. Carbon dioxide is a greenhouse gas of major concern in the study of global warming. It is estimated that the amount in the air is increasing by 0.4% annually. Anthropogenic carbon dioxide is emitted mainly through the burning of fossil fuels and deforestation.

Vegetation consisting of broadleafed evergreen shrubs, found in regions of Mediterranean-type climate of hot, dry summers and mild, wet winters.

chlorofluorocarbons (CFCs)
Synthetically produced compounds containing varying amounts of chlorine, fluorine, and carbon. they are used in industrial processes and as a propellant for gases and sprays. In the atmosphere they are responsible for the depletion of ozone. One molecule can destroy as many as 10,000 molecules of ozone in their long lifetime. Their use is now restricted under the Montreal Protocol.

The prevalent long-term weather conditions in a particular area. Climatic elements include precipitation, temperature, humidity, sunshine, and wind velocity. Climate cannot be considered a satisfactory indicator of actual conditions, since it is based upon a synthesis of a vast number of elements taken as an average.

climate change
This strictly refers to all forms of climatic inconsistency, but since climate is never a static figure and is based on an aggregate, the term is often used in a more restricted sense to imply a significant change over the long term. Within the media, climate change has been used synonymously with global warming.

climate feedback
A secondary process resulting from primary climate change which may increase (positive feedback) or diminish (negative feedback) the magnitude of climate change.

Practices or processes that result in long-term change in land use to nonforest uses. This is often cited as one of the major causes of the enhanced greenhouse effect, for two reasons: (a) the burning or decomposition of the wood releases carbon dioxide; and (b) trees that once removed carbon dioxide from the atmosphere in the process of photosynthesis are lost.

The reduction of nitrates and nitrites to nitrogen by microorganisms.

electromagnetic waves (EM)
or Electromagnetic Radiation is a type of wave consisting of both a magnetic and electric component. The purpose of EM waves is to carry energy from one place to another. They are characterized by their frequency or wavelength. Some types of EM waves are radio and TV, microwaves, infrared, ultraviolet, X-rays and visible light.

El Niño
A climatic phenomenon occurring every 5 to 7 years during the Christmas season (El Niño means Christ child) in the surface oceans of the southeast Pacific. The phenomenon involves seasonal changes in the direction of Pacific winds and abnormally warm surface ocean temperatures. The changes normally only affect the Pacific region, but major El Niño events can disrupt weather patterns over much of the globe. The relationships between these events and global weather patterns are poorly understood and are currently the subject of much research.

The release of a substance (usually a gas, when referring to climate change) into the atmosphere.

The capacity to do work.

forcing mechanism
A process which alters the energy balance of the climate system, for example, changes the relative balance between incoming solar short-wave radiation and outgoing longwave radiation from Earth. Such mechanisms include changes in solar output and the enhanced greenhouse effect.

fossil fuel
Any hydrocarbon deposit that can be burned for heat or power, such as coal, oil, or natural gas. Fossil fuels are formed from the decomposition of ancient animal and plant remains. A major concern is that they emit carbon dioxide into the atmosphere when burned.

global warming
A theory that increased concentrations of greenhouse gases are causing an elevation in Earth's surface temperature.

global warming potential (GWP)
An index used to approximate the effect of an instantaneous release of a unit mass (1 kg) of a greenhouse gas in atmosphere, relative to that of carbon dioxide. The index takes into the account the lifetime of the gas and describes the relative effectiveness of the gas in contributing to global warming.

greenhouse effect
A term used to describe the effect wherein greenhouse gases trap re-emitted infrared radiation from Earth, thus heating the atmosphere. This is a natural phenomenon and increases Earth's average surface temperature from -18C (the effective radiation temperature) to +15C. This should not be confused with the enhanced greenhouse effect, the increase of the greenhouse effect as a result of human activities.

greenhouse gases
Water vapor, carbon dioxide, tropospheric ozone, nitrous oxide, methane, and other lesser gases in the atmosphere. They allow short-wave ultraviolet (UV) radiation to pass through unimpeded, but trap longwave infrared radiation re-emitted from Earth. Water vapor is the most important greenhouse gas, but concentrations in the atmosphere are believed to be little affected by human activity. This is not the case with carbon dioxide, methane, and nitrous oxide, where human activity is leading to increased levels of these gases in the atmosphere and enhancing the natural greenhouse effect.

infrared radiation
Electromagnetic radiation of lower frequencies and longer wavelengths than visible light (greater than 0.7 microns (µm)). Solar ultraviolet radiation is absorbed by Earth's surface and re-emitted as infrared radiation.

Intergovernmental Panel on Global Climate Change (IPCC)
A scientific body established in 1988 by the UNEP (United Nations Environmental Programme) and WMO (World Meteorological Organisation) with three main objectives. The first is to assess the available scientific information on climate change, the second to assess the environmental and socioeconomic impacts of climate change, and the third to formulate response strategies. The group played a large part in the formulation of a U.N. framework convention on climate change, signed in 1992, and has produced two assessment reports, the first in 1990 and the second in 1994.

The amount of an element or compound which contains 6.023 X 1023 atoms or molecules.

old-growth forest
Forest that has not been cut or disturbed by humans for hundreds of years.

ozone (O
Ozone consists of three atoms of oxygen bonded together, in contrast to normal atmospheric oxygen, which consists of two atoms of oxygen. Ozone is formed in the atmosphere and is extremely reactive and thus has a short lifetime. In the stratosphere, ozone is both an effective greenhouse gas (absorber of infrared radiation) and a filter for solar ultraviolet radiation. Ozone in the troposphere can be dangerous, since it is toxic to human beings and other living matter. Elevated levels of ozone in the troposphere exist in some areas, especially large cities as a result of photochemical reactions of hydrocarbons and nitrogen oxides, released from vehicle emissions and power stations.

In an elliptical orbit, it is the point of closest approach the sun.

radiactive forcing
A variation in the balance of energy absorbed by Earth and that emitted by it. This can be due to natural causes, such as variation in the solar output, or by anthropogenic causes, such as the enhanced greenhouse effect. Positive radiative forcing has the effect of warming the surface of the Earth, while negative forcing has a cooling effect.

A tropical grassland, usually scattered with trees or shrubs.

Stefan's law
Describes the relationship between the rate of energy radiated, as electromagnetic waves, and the temperature of the object.

P = sAeT

P is the rate of energy radiated or power in Watts = joules/s
s is the Stefan-Boltzmann constant = 5.67 X 10-8 W/m2K4
A is the surface area of the object in m2
e is the emissivity and is a characteristic of the material. Dark surfaces have emissivities close to 1, and shiny surfaces have emissivities close to 0. Emissivity is unitless.
T is the temperature of the object in degrees Kelvin

swamp A wooded wetland in which water is near or above ground level.

The northern circumpolar boreal forest.

temperate rain forest
Forests in regions with mild climate and heavy rainfall that produce lush vegetative growth; one example is the coniferous forest of the Pacific Northwest of North America.

total solar irradiance
Describes the radiant energy emitted by the sun over all wavelengths that falls each second on 1 square meter just outside Earth's atmosphere.

A unit of power output or energy output per unit time (joules per second)

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